High-frequency amplifying circuit arrangement



1949. M. J. o STRUTT ET AL Q 7 HIGH-FREQUENCY AMPLIF'YING CIRCUIT ARRANGEMENT Filed May 1, 1946 FIG. 2

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A W a FIGS VT MAXIMILIAAN JULIUS OTTO STRUTT Patented Aug. 2, 1949 HIGH-FREQUENCY AMPLIFYING CIRCUIT ARRANGEMENT Maximiliaan Julius Otto Strutt and Aldert van der Ziel, Eindhoven, Netherlands, assig-nors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application May 1, 1946, Serial No. 666,246 In the Netherlands August 5, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires August 5, 1961 9 Claims.

The specification of U. S. Patent No. 2,352,956, issued July 4, 1944, jointly to the present inventors and Cornelis Jan Bakker, describes a circuit arrangement for the transmission of high-frequency electrical oscillations which comprises at least one controlled discharge tube and is equipped with a resonant input circuit which is so proportioned that the natural losses of this circuit involve a smaller damping than is necessary and the required damping is at least substantially brought about by withdrawing energy from the circuit by means of negative back coupling, the backcoupling current or voltage being taken from the circuits of one or more current carrying electrodes which are so chosen that the negative backcoupling at the same time reduces the noise current in the output circuit.

It is the object of the invention to provide novel methods for controlling the amplification of circuits of the type above-described.

In the circuit arrangement according to the above-mentioned patent the problem of controlling the amplification of the circuit arises. In eifect, when controlling the amplification in the usual way by modifying the bias of the control grid the degree of negative backcoupling decreases with a decrease in amplification, due to which the control is not effective on the one hand. and the selectivity increases on the other hand, so that in receiving strong signals, with which the amplification is small, the selectivity is very high.

According to the invention this drawback is obviated since the amplification is controlled by variation of the degree of negative backcoupling. Preferably the bias of the input electrode of the discharge tube is varied at the same time in such manner that this bias becomes more negative with an increase in negative backcoupling.

The invention will be more fully explained by reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of a circuit arrangement in accordance with the invention,

Figure 2 is a schematic diagram illustrating another embodiment in accordance with the invention, and

Figure 3 is a schematic diagram illustrating a further embodiment in accordance with the invention.

Fig. 1 shows a high-frequency amplifying circuit which may be used, for instance, in a first stage of a radio receiver. A resonant circuit l tuned to the signal to be transmitted is inserted in the control grid circuit of a tube 2. The anode circuit of the tube comprises a circuit 3 which is tuned to the same frequency and from which the amplified voltage is taken. The circuit l is so constructed that its natural damping is smaller than is necessary in conjunction with the band width to be transmitted. A part of the energy set up in the anode circuit 3 is supplied through a coil 4| to the first control grid of an octode 42. The voltage thus set up at the first anode 43 of this tube is supplied through a coil 44 to the circuit l in such a phase that the latter is damped thereby and the selectivity of this circuit is consequently decreased. The second anode 45 of the octode is connected to the cathode through the intermediary of a source of potential 41. To the second control grid 45 of the octode is supplied a control voltage Vr whose value depends on the average amplitude of the oscillations to be transmitted. The electrode 45 controls the distribution of current between the second anode 4B and the first anode 43 in such manner that the current to the electrode 43 and consequently the degree of negative feedback increases with an increase in negative control voltage. Due to this the amplitude of the signal appearing in the output circuit 3 decreases thus ensuring effective gain control. At the same time the range of transmission of the input circuit increases on account of the increasing damping thereof so that the selectivity decreases. Consequently, the selectivity of the circuit will decrease with an increase in signal voltage.

Although this relationship between selectivity and amplification frequently ofiers advantages it may sometimes be undesirable and often the attempts are directed to obtaining a substantially constant damping of the input circuits. According to the invention this can be achieved by modifying the degree of negative backcoupling and in addition the value of the control grid bias of the tube for controlling the amplification. Fig. 2 represents a circuit in which this method is used. The circuit shown in Fig. 2 substantially corresponds to that shown in Fig. 1. However; it comprises a grid condenser 3| and a leakage resistance 32 through which the control voltage V1 is supplied also to the control grid of tube 2. The operation is as follows:

With an increase in negative bias applied through the resistance 32 the voltage set up across the output circuit 3 of the tube 2 is reduced so that a lower voltage is applied to the first control grid of the auxiliary tube 42. The negative bias supplied to the control grid 45 of the auxiliary tube increases at the same time as a, result of which the mutual conductance towards the electrode 43 is increased. Thus the voltage induced in the coil M decreases on the one hand, but on the other hand the amplification of that part of the tube 42, which is constituted by the cathode, the first control grid and the anode 43. increases with an increase in negative bias of the grid 45, so that by giving the circuit elements suitable proportions the voltage set up in coil 46 will be substantially independent of the control voltage. Owing to this the damping of the circuit l and consequently its selectivity remain-constant and yet the voltage set up in the circuit 3 decreases with an increase in control voltage. Fig. 3 represents another embodiment of the invention in which the use of an. auxiliary tube is eliminated. In this case use is made of an .octode 52 to whose first control grid 54 is connected a circuit l which is tuned to the oscillations to be transmitted. The natura1 damping of this circuit is deliberately chosen too low in proportion. to the desired range of transmission, and the additional damping thus required is: brought abou by- .ccupling in a correctmanner a coil .53, which is inserted in the external circuit of .the geeond grid 55,. with the coil or the circuit I. Eire anode circuit-comprises a circuit 3. which is tuned til the :irequency :of the oscillations: to, be transmitted andirom which theamplified voltage is taken. A variable negative bias Vr is supplied 'bottrto the, first: control grid 54- and tothe second controlgrid 5.5.

the operation of the-circuit is as tollowstwith aniincrease in negative bias-V1? on the first cong-rid 54 the current. having the signal freoucncy'through. the-coil. 53 and consequently also the negative. feedback will decrease in the first instance. Since, however, the. secondcontrol grid zI5,.wlai-chacts as a current distribution-grid. also becomes more negative the current traversing the coin will jrustztendto increase. With a suitable ratio ofthe control volta es supplie to h two control grids-in cortiunction with the mutual conductances ofthe two grids it can be achieved that the current the coil 53 and consequently the damping of the circuit is at least substantially independent of variations of. the control voltage; whilst neve,rtl'reless-- obtaining a very efreactive gain. control.

Whatwe-claim is:

it. A; circuit. for transmitting a band of electric oscillations, comprising an electron discharge tube having a cathode, a first: con twig-rid; a, perforated anode,.a second con-trol'grid anda second anode, a-resonantinputcircuit having a natural dampin smaller necessary loathe width; of band of electric. oscillations, means to apply said electric oscillations to said inpwtiescnant circuit,.means to -apply said electricoscillati'ons to. sai first. control gr mean coupling perforated; anode torsaid input resonant circuit: in. ne tive ,feedback. relationship and means to apply a control. voltage varying. in amplitude. proportional. to: the amplification .of said: circuit arrangement to. .saidsecond control grid to. vary- .the degree oi teedback' and to. in-

crease the dampingof. said! input circuit and thereby control the amplification oi said circuit arrangement- 2..A arrangement for transmitting: a "band: or electric oscilrlatioms', comprising. n el ctron discharge tube having a cathode, afirst conof electric oscillations, means to apply said electric oscillations to said resonant input circuit, a resonant output circuit, means couplin said first control grid to said resonant output circuit, means coupling said perforated anode to said resonant input circuit in negative feedback relationship, and means to apply a control voltage varying in amplitude proportional to the amplification of said circuit arrangement to said second control grid to vary the degree of feedback and to increase the damping of said input circuit and thereby control. the amplification of said circuit arrangement.

3. A circuit arrangement for transmitting a bandof electric oscillations, comprising an electron discharge tube havin a cathode, a first con trolgrid, a perforated anode, a second control grid and a second anode, a resonant input circuit having a natural damping smaller than necessary for the width of said band of electric oscillations, means. to apply said electric oscillations to said resonantinput circuit, a resonant output circuit, means coupling said first control grid to said res.- onant-output circuit, means coupling said perforated anodeto said resonant input circuit in negative feedback. relationship, and. means to apply a control voltage. varying in amplitude proportional tov the. amplification of said circuit arrangement to said first and saidv second control grids to vary the degree of feedback and to increase the. damping of said resonant. input circuit and thereby control the amplification of said circuit arrangement.

4. A circuit arrangement for transmitting a bandcf electric oscillations, comprising an electron discharge tubehaving a cathode, a first control grid, a perforated anode, a second control grid anda secondanode, a. resonant input circuit having, anatural damping smaller than necessary for the width of said-band. of. electric oscillations, means to apply said electric. oscillations to said resonant inputcircuit, a resonant output circuit. means coupling, said first controLgri-d'. to said res!- onan-t output circuit, means coupling said periorated anode to said resonant. input circuit in neg- .ative feedback relationship, and. means to apply a control voltage-varying in amplitude proportional totheamplification. of said circuit arrangement tosaidfirst and said secondcontrol grids to vary the-degree of feedback and. toincrease the damp- 'i-ng' of said resonant input circuit and. thereby control the. amplification-of said circuit. arrangement, said first control grid being negatively increased With increasing negative feedback.

5. A circuit arrangement for transmittin a band of electric oscillations, comprising .anelectron. discharge tube having a cathode, ;a first. control grid, a perforated anode, a. second control grid and-a second anode, a resonant input circuit'having; anatural damping smaller than. necessaryfor thewidth oi. said band of electric oscillations, meansto apply said electric oscillations to. said resonant input. circuit, a resonant output. circuit, means coupling said first control grid to said resonant output circuit, means coupling said perforatedanode to. said. resonant. input circuit inv negative feedback. relationship, and. means to. apply a control voltage varying in amplitude proportional to the. amplification of. said circuit. arrangement to. said first andsaid. second control gridsto vary the degree. offeedback and to. vary the damping of said resonant, input. circuit and thereby control the amplification of said circuit arrangement, saidfirst control grid being negatively increased. with increasing negative feedback to maintain the damping of said resonant circuit substantially constant over the Width of said band of electric oscillations.

6. A circuit arrangement for amplifying a band of electric oscillations, comprising an electron discharge amplifier tube having a cathode, a signal grid and an output electrode, an electron discharge control tube havin a cathode, a first control grid, a perforated anode, a second control grid and a second anode, a resonant input circuit having a natural damping smaller than necessary for the width of said band of electric oscillations, means to apply said electric oscillations to said input resonant circuit, means coupling said resonant input circuit to said signal grid, a resonant output circuit coupled to said output electrode, means coupling said output resonant circuit to said first control grid, means coupling said perforated anode to said input resonant circuit in negative feedback relationship, and means to apply a control voltage varying in amplitude proportional to the amplification of said circuit arrangement to said second control grid to vary the degree of feedback and to increase the damping of said resonant input circuit and thereby control the amplification of said circuit arrangement.

'7. A circuit arrangement for amplifying a band of electric oscillations, comprising an electron discharge amplifier tube having a cathode, a signal grid and an output electrode, an electron discharge control tube having a cathode, a first control grid, a perforated anode, a second control grid and a second anode, a resonant input circuit having a natural damping smaller than necessary for the width of said band of electric oscillations, means to apply said electric oscillations to said input resonant circuit, means coupling said resonant input circuit to said signal grid, a resonant output circuit coupled to said output electrode, means coupling said output resonant circuit to said first control grid, means coupling said perforated anode to said resonant input circuit in negative feedback relationship, and means to apply a control voltage varying in amplitude proportional to the amplification of said circuit arrangement to said signal grid and to said second control grid to vary the degree of feedback applied t0 said amplifier tube and to increase the damping of said resonant input circuit and thereby control the amplification of said amplifier tube.

8. A circuit arrangement for amplifying a band of electric oscillations, comprising an electron discharge amplifier tube having a cathode, a signal grid and an output electrode, an electron discharge control tube having a cathode, a first control grid, a perforated anode, a second control grid and a second anode, a resonant input circuit having a natural damping smaller than nii necessary for the width of said band of electric oscillations, means to apply said electric oscillations to said input resonant circuit, means coupling said resonant input circuit to said signal grid, a resonant output circuit coupled in said output electrode, means coupling said ouput resonant circuit to said first control grid, means coupling said perforated anode to said resonant input circuit in negative feedback relationship, and means to apply a control voltage varying in amplitude proportional to the amplification of said circuit arrangement to said signal grid and to said second control grid to vary the degree of feedback applied to said amplifier tube and to vary the damping of said resonant input circuit and thereby control the amplification of said amplifier tube, said signal grid being increasingly negative with increasing negative feedback to maintain the damping of said resonant input circuit substantially constant.

9. A circuit arrangement for amplifying a band of electric oscillations, comprising an electron discharge amplifier tube having a cathode, a signal grid and an output electrode, an electron discharge control tube having a cathode, a first control grid, a perforated anode, a second control grid and a second anode, a resonant input circuit having a natural damping smaller than necessary for the width of said band of electric oscillations, means to apply said electric oscillations to said input resonant circuit, means coupling said resonant input circuit to said signal grid, a resonant output circuit coupled in said output ,electrode, means couplin said output resonant circuit to said first control grid, means coupling said perforated anode to said resonant input circuit to couple the same to said resonant output circuit in negative feedback relationship, and means to vary the amplification of said control tube to vary the degree of feedback from the output circuit to the input circuit of said amplifier tube to vary the damping of said resonant input circuit and thereby control the amplification of said amplifier tube to maintain the damping of said resonant input circuit substantially constant.

MAXIMILIAAN JULIUS OTTO STRUTT. ALDERT VAN DER ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,152,618 Wheeler Mar. 28, 1939 2,208,665 Cra'btree M July 23, 1940 2,304,978 White Dec. 15, 1942 2,315,043 Boucke Mar. 30, 1943 2,343,207 Schrader Feb. 29, 1944 

